1. Field of the Invention
The present invention relates to a cryogenic refrigerator, and more specifically to a cryogenic refrigerator including a displacer.
2. Description of the Related Art
Conventionally, a Gifford McMahon refrigerator (which is called hereinafter “GM refrigerator”) is known as a cryogenic refrigerator including a displacer. This GM refrigerator is configured to allow the displacer to move back and forth in a cylinder by a drive unit.
Moreover, an expansion space is formed between the cylinder and the displacer. By allowing the displacer to move back and forth in the cylinder, a refrigerant gas that is supplied to the expansion space is expanded, so that a cryogenic cooling is generated.
In general, in this kind of GM refrigerator, a moving speed of one cycle in which the displacer moves back and forth at one stroke in the cylinder is set to be the same as a speed of a simple harmonic motion.
Generally speaking, the displacer is in the vicinity of the bottom dead center, and the GM refrigerator performs a process that suctions a high-pressure refrigerator gas into the cylinder.